To meet the demand for wireless data traffic having increased since deployment of 4th generation (4G) communication systems, efforts have been made to develop an improved 5th generation (5G) or pre-5G communication system. Therefore, the 5G or pre-5G communication system is also called a ‘Beyond 4G Network’ or a ‘Post LTE System’.
The 5G communication system is considered to be implemented in higher frequency (mmWave) bands, e.g., 60 GHz bands, so as to accomplish higher data rates. To decrease propagation loss of the radio waves and increase the transmission distance, the beamforming, massive multiple-input multiple-output (MIMO), Full Dimensional MIMO (FD-MIMO), array antenna, an analog beam forming, large scale antenna techniques are discussed in 5G communication systems.
In addition, in 5G communication systems, development for system network improvement is under way based on advanced small cells, cloud Radio Access Networks (RANs), ultra-dense networks, device-to-device (D2D) communication, wireless backhaul, moving network, cooperative communication, Coordinated Multi-Points (CoMP), reception-end interference cancellation and the like.
In the 5G system, Hybrid FSK and QAM Modulation (FQAM) and sliding window superposition coding (SWSC) as an advanced coding modulation (ACM), and filter bank multi carrier (FBMC), non-orthogonal multiple access (NOMA), and sparse code multiple access (SCMA) as an advanced access technology have been developed.
The rapid developments of information industries, especially, the increasing demands from mobile Internet and Internet of things (IoT), bring unprecedented challenges to the mobile communications technologies. As reported in ITU-R M. [IMT.BEYOND 2020.TRAFFIC] from the International Telecommunication Union (ITU), the mobile traffic is expected to grow by nearly 1000 times from year 2010 (in the era of fourth-generation (4G)) to 2020, and the number of the user device connections will surpass 17 billion. As a large amount of IoT equipment gradually penetrate into the mobile communication network, the number of the device connections will become more massive. In order to cope with these unprecedented challenges, the fifth-generation (5G) mobile communications technologies are being under research in the communication industries and in the academic community, facing the year of 2020. Currently, the framework and overall objectives of future 5G are being discussed in the report ITU-R M. [IMT.VISION], in which demand prospects, application scenarios and a variety of key performance requirements are described below. For new demands of 5G, the report of ITU-R M.[IMT.FUTURE TECHNOLOGY TRENDS] provides relevant information on trends of 5G, intending to address significant issues, such as a sharp increase of the system throughput, user experience consistency, scalability to support IoT, latency, energy efficiency, cost efficiency, flexibility of networks, new services' support, flexible spectrum usage and the like.
Modulation waveforms and multiple access schemes are important for designing air-interface of mobile communications, and 5G is no exception. Currently, orthogonal frequency division multiplexing (OFDM), which is a typical representative in the family of multi-carrier modulation (MCM), is widely used in broadcast audio and video fields as well as in civil communication systems, for example, evolved universal terrestrial radio access (E-UTRA) protocols defined by the third generation partnership project (3GPP) which corresponds to the system of long term evolution (LTE), digital video broadcasting (DVB) and digital audio broadcasting (DAB), very-high-bit-rate digital subscriber loop (VDSL), IEEE802.11a/g wireless local area network (WLAN), IEEE802.22 wireless regional area network (WRAN) and IEEE802.16 world interoperability for microwave access (WiMAX) and the like. The idea of OFDM is to divide a wide channel into a plurality of parallel narrowband sub-channels/subcarriers so that high-speed data flows transmitted in frequency selective channels are converted to low-speed data flows transmitted in a plurality of parallel independent flat-fading channels, thereby capabilities of the system to counter multipath interferences are greatly improved. Furthermore, OFDM can utilize inverse fast fourier transform/fast fourier transform (IFFT/FFT) to implement simplified modulation and demodulation modes. Moreover, the insertion of cyclic prefix (CP) converts a channel effect from a linear convolution to a circular convolution. As a result, according to the properties of a circular convolution, when the length of CP is greater than the largest multipath time delay, the signals can be received without inter-symbol interference (ISI) by applying simple one tap frequency-domain equalization, which in turn reduces processing complexity of receivers. Although modulation waveforms based on CP-OFDM are capable of meeting the service demands of mobile broadband (MBB) in the era of 4G, there are many limitations and shortcomings for CP-OFDM application in 5G scenarios since 5G will have to face more challenging and diversified scenarios, which mainly comprises the following scenarios:
(1) The insertion of CP for resisting ISI will greatly reduce spectrum utilization in 5G scenarios of low latency transmissions. To be specific, the low latency transmissions will greatly shorten the length of OFDM symbols and the length of CP is only constrained by the impulse response of channels, and thus the ratio of the length of CP and the length of OFDM symbols will increase greatly. Such overhead results in loss of spectrum efficiency largely and thus is unacceptable.
(2) Strict requirements on time synchronization will result in large signaling overheads required for maintaining the closed loop synchronization in IoT scenarios of 5G. In addition, the strict synchronization mechanism makes data frame structure nonflexible, and thus cannot satisfy the different synchronization requirements of a variety of services.
(3) OFDM adopts rectangular pulse such that the frequency domain sidelobe rolls off very slowly, which causes large out-band leakage. Therefore, OFDM is very sensitive to the carrier frequency offset (CFO). While there will be many demands for fragmented spectrums flexibly access/share in 5G, the high out-band leakage of OFDM greatly limits flexibilities of spectrum access or it needs large frequency-domain protection band, such factors reduce the spectrum utilization accordingly.
These shortcomings are mainly due to OFDM characteristics. Although the impacts caused by these shortcomings can be reduced by adopting certain measures, the shortcomings will increase the complexity of system designs, and these issues cannot be addressed.
Just due to the issues mentioned above, as reported in ITU-R M. [IMT.FUTURE TECHNOLOGY TRENDS], some new waveform modulation technologies (multi-carrier modulation based) are taken into account in 5G, of which filter bank multiple carrier (FBMC) modulation becomes one of the main research objects. As FBMC provides free degrees for designing prototype filter, FBMC can utilize the filters with high performance on time/frequency localization (TFL) to shape pulse of transmission waveforms, such that the transmission signals can show various preferable characteristics, comprising improvement of the spectrum efficiency since no requirements on CP insertion is needed to resist ISI, lower out-band leakage to support flexible access of fragmented spectrums and the insensitiveness to carrier frequency offset. The typical FBMC generally uses a technology named offset quadrature amplitude modulation (OQAM) to maximize the spectrum efficiency. Therefore, such technology is generally called FBMC/OQAM system, also called OFDM/OQAM system. The FBMC applications in digital communications have been discussed in an early article titled as “Analysis and design of OFDM/OQAM systems based on filter bank theory” (IEEE Transactions on Signal Processing, Vol. 50, No. 5, 2002).
Because FBMC has some advantageous characteristics which OFDM does not possess, FBMC gets more attention in 5G research, but some inherent shortcomings challenge FBMC applications in mobile communications, and these challenges need to be addressed urgently and are studied constantly. One of these significant issues is that the filters adopted in FBMC can cause a longer tail effect which is also called as a transition period issue. During the uplink multi-user transmission based on short data blocks (data frames), if the length of the data blocks comprises tail effect to avoid overlapping between the tail and other data blocks, the number of symbols transmitted within active time would decrease, thereby reducing the spectrum efficiency. Therefore, some people hold that FBMC is only suitable for long burst of data transmission. In contrast, if the length of the data blocks does not comprise the tail effect, portions of the tail would overlap with other data blocks (especially with the data blocks from other users), and it would cause serious inter-block interferences if it is not addressed properly, thereby further reducing the spectrum usage efficiency. In addition to multiuser interferences, in time division duplexing (TDD) system, the uplink/downlink transition period also needs to be increased properly to avoid unnecessary uplink/downlink crosstalk generated by the tail effect, which further reduces the spectrum efficiency of the system. Currently, the existing method is to truncate portions of the tail to avoid overlapping with other data blocks. However, truncating waveforms causes a distortion of signals, which can also impact the spectrum efficiency. Moreover, the spectrum of truncated signals extend, generating inter-carrier interference (ICI). Accordingly, such direct truncation is not effective.
In conclusion, in order to improve the competitiveness of FBMC among candidate technologies, it is required to address the inherent shortcomings in addition to developing the advantageous characteristics. For service modes of sporadic access in various scenarios of 5G, especially in IoT scenarios, it is necessary to use an efficient method to address issues caused by the tail effect of FBMC in the mobile communications system.
With respect to the tailing issue in the FBMC system when a data block is transmitted, there is not yet an effective method for reducing the influence on a system brought by a smearing effect. Therefore, the present disclosure provides an effective method for restraining tailing, which can reduce an additional consumption brought by the smearing effect while high signal receiving performance and frequency spectrum leakage characteristics can be ensured such that a frequency spectrum efficiency of the FBMC system can be maximized.
The above information is presented as background information only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present disclosure.